1. Field of the Invention
The present invention relates to an automatic original feeding and discharging unit, more specifically, it relates to an automatic original feeding and discharging unit which is, when copying an original with an image forming apparatus such as an electrophotographic copying machine, capable of feeding the original on an original table of said copying machine so as to be placed at a prescribed position thereon, and discharging said original from the original table when the copying operation is completed.
2. Description of the Prior Art
In a copying machine such as an electrophotographic copying machine, an original to be copied is placed on an original table using a contact glass or the like to form a copy image of the original by an electrophotographic process. In such copying machine, when a plurality of originals are copied, an automatic original feeding and discharging unit which feeds the originals to be copied successively on the original table and discharges the originals which have bee copied successively from the original table is used.
In the conventional automatic original feeding and discharging unit, after the original is transferred to a prescribed position on the original table by a transfer belt extending from one side to the other side above the original table, the transfer belt is stopped temporarily for positioning the original. After the original has been copied, the transfer belt is driven again to discharge the original from the original table. In the conventional automatic original feeding and discharging unit thus constructed, due to the expansion and contraction of transfer belt or the difference of friction coefficient on the surface thereof the original can not be stopped surely at the prescribed position in a prescribed attitude, so that the original is apt to shift from its prescribed position on the original table. When the original to be transferred is not placed properly on the original table before transfer, it is transferred as it is, thus also in this case the original is apt to be placed improperly on the original table. Since the original is transferred by the transfer belt only in the fixed direction, when a large size original of, for example, A2 size is to be fed or discharged to and from the original table, the transfer belt must be enlarged.
In order to solve such problem, an automatic original feeding and discharging unit which feeds and discharges the original to and from the original table by rollers without using the transfer belt is disclosed in Japanese Patent Publication No. 41825/1974.
In the automatic original feeding and discharging unit disclosed in Japanese Patent Publication No. 41825/1974, the original is positioned at the prescribed position on the original table in such a manner that, the original is first fed to the original table by the transfer roller and when the original arrives at the prescribed position on the original table, said transfer roller is detached from the original to stop transferring the original. Therefore, in order to stop the original in the prescribed attitude at the prescribed position on the original table, timing or the like for detaching the original transfer roller from the original must be controlled very precisely. Since the friction coefficient between the original and the original table is not always constant, the original detached from the original transfer roller at the prescribed timing does not always stop at the prescribed position on the original table, but likely to shift therefrom due to the paper quality of the original. Moreover, the original is transferred to the original table in parallel movement and its attitude is not corrected on the original table, so that if it is not in the prescribed attitude in the beginning it will never be placed on the original table in the prescribed attitude. It is thus very difficult to place the original surely in the prescribed attitude at the prescribed position on the original table by the automatic original feeding and discharging unit disclosed in Japanese Patent Publication No. 41825/1974. In addition, the original having original faces on both sides can not be placed so as to bring the original face in contact with the original table successively.
Another prior art is disclosed in U.S. Pat. No. 4,428,666. In this U.S. Patent, a registration edge which is possible to project and plunge is provided so as to position the original at the prescribed position on the original table. A reversing mechanism is also provided for copying the original having two original faces. In this prior art, however, a pair of rollers which contact to the original on the original table for transfer are designed to transfer only in one direction, so that when one side of the original has been copied the original is once discharged and returned to the original stocker and fed once again after one side of remaining originals have been copied. At this time, the original is directed to the reversing mechanism and after being oriented by a diverter on the way, transferred reversely in the opposite direction to the original table for copying operation of the other side, thus a very long transferring path is required for copying both sides, which is not only time consuming but also the unit itself become complex and it is difficult to make it compact.